Locally acting intestinal aminosalicylate
ATC code: A07EC02 (Mesalazine)
Brand names
Asacol, Salofalk, Mezavant, Claversal
Pure 5-aminosalicylic acid (5-ASA). Acts locally on colonic mucosa: inhibits prostaglandin and leukotriene synthesis, neutrophil migration to inflammation sites, and NF-κB. Compared with sulfasalazine, no sulfapyridine component – fewer systemic side effects. Various formulations target specific bowel segments: granules and tablets with pH-dependent release (Asacol, Pentasa), time-dependent (Salofalk), enemas and suppositories for distal colitis and proctitis.
First line
First-line for mild-to-moderate ulcerative colitis to induce and maintain remission per 2024 and the Spanish GETECCU 2023. Induction 2.4–4.8 g daily in 2–3 doses; maintenance 1.5–2.4 g daily. In distal colitis and proctitis, add enemas 4 g once daily or suppositories 1 g once daily. The 2020 Cochrane meta-analysis showed remission induction in 50–60% and 2–3-fold reduction in relapse risk.
The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.
Not recommended
Mesalazine (5-aminosalicylic acid, 5-ASA) is an anti-inflammatory drug for inflammatory bowel disease. It is prescribed for ulcerative colitis and Crohn's disease with colonic involvement ( 2024, 2024). For intestinal dysbiosis, mesalazine is not indicated: dysbiosis is not recognized as an independent diagnosis in immunocompetent people in international medicine, with no agreed diagnostic criteria. The drug has specific risks: nephrotoxicity (requires renal function monitoring), hepatotoxicity, myocarditis and pericarditis (rare), pancreatitis, and severe skin reactions. If mesalazine was prescribed for dysbiosis outside ulcerative colitis or Crohn's disease, consider seeking a second opinion.
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FDA category B. Large pregnancy data set without described teratogenic effects. Used when indicated in all trimesters.
Compatible with breastfeeding. Low systemic bioavailability, minimal milk concentrations. Transient infant diarrhea is possible.
Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.
Mesalazine is evaluated for the following indications with varying evidence strength: Ulcerative colitis (evidence tier A), «Gut dysbiosis» as a standalone clinical diagnosis (evidence tier F). See the full indication matrix with dosing and citations above on this page.
Common side effects of Mesalazine (≥ 1 in 100): Headache, Nausea, diarrhea, Abdominal pain, Skin rash, Fatigue. See the Safety section for uncommon and serious reactions.
FDA category B. FDA category B. Large pregnancy data set without described teratogenic effects. Used when indicated in all trimesters.
Compatible with breastfeeding. Low systemic bioavailability, minimal milk concentrations. Transient infant diarrhea is possible.
Mesalazine is contraindicated in: Mesalazine or salicylate hypersensitivity; Severe hepatic or renal impairment; Active peptic ulcer; Age under 6. Full list in the Safety section.